X-ray tube and cathode therefor



March5, 1935. c. T. ULREY X-RAY TUBE AND CATHODE THEREFOR Filed March 28, 1953 INVENTOR 6T 7:' ULE'Y Bw 9% ATTORNEY Patented Mar. 5, 1935 UNITED. sTAT Aiii-RAY TUBE AND -oATHoDE THEREFon Clayton'lridle `Ulre'y, EastOrange N. J assigner i to Westinghouse Lamp Company, a corporation fof Pennsylvania Applation Maren 2s, 193s, serial No. 663,107 f t 5 Claims. y(Cl. Z50-35) 5 a InV its'more' specic aspect the invention is directed to improvedmeans adapted Vto produce a; focal spot on the anodev target of a tube'of this character; 'Heretofore X-ray tubes containing an ianode and'afcathode Within an evacuatedV envelope have been employed in a number of different elds, including the therapeutic,l radiographic and industrial fields.V X-ray tubesvemployed in these Vfields have contained cathode structures of one type or another. K f

Prior to ther time of this invention it hasbeen proposed to employ al cathode structure consisting ofxacup in-which-is mounted a'spirally wound filament through the center of which extends an elongated thin pinladapted to -deflect the electrons which emanatefrom the-filament.

In the course of Vmy experimentations: with cathode structures of the above v'noted character, and especially such structures when employed in X-ray tubes, I have found thatwith such a cathode structure the Vfocal spot produced on the target of an X-ray tube consists of an annular spot with aY spot of appreciable areaat-the center thereof. The spot in -the centerl of the annular spot was objectionable. f Y Y 1 In order that I might overcome the` diiuculties .inherent in the heretofore employed ,cathode structures and 'especially those employed-in X- ray tubes vI havedeveloped the followinginvention, which will hereinafterbemore fully disclosed. Y

Y' An objectof:- my invention-is to provide an X- ray tube, having advantages over those now em- D10Yed---. i -1 Anotherobject of Ymyinvention is to provide a vnewV type of cathode structure. y

Another object of my invention is to provide an improved cathode for obtaining an annular focal spotv with no spot in the center thereof.

. Other objects and advantages of my invention will Ybe Yreadily apparent from the following description' and drawing wherein; y v' A Figure 1 illustrates a shortened fragmentary view with lsome Aof the parts :inI elevation and others in cross section of an. X- ray tube embodying my invention;

Figure 2 represents a cross sectional View taken along lines II-II of Figurel; r Figure 3 represents a cross sectional View showingjthe improved cathode structure as mounted and the relationship-of cathode structure; I Y c Y.

Figure 4 representsa plan view of the `cathode structure taken in the direction of the large end of the cathode cup; Y ,Y -g i Figure 5 :representsnthe focal spot obtained by employingjthe structure shownin Figure `1*;

Figure' 6 represents the focal spot obtained -by employing a modifiedffocusing cup havingv no cutouts and employedinthe position showny -in Figure l.

ES PATENT-OFH'C.fl

`the different parts to thel 4Figures 7 and-8representthetype'offocal'spots obtained with some prior art.` cathode structures. As shownthe X-ray tube comprises a vitreous dielectric envelope 10 in Whichis located an anode 11 having a target 12 composedqof tungsten or the like and embedded inthe free endthereof; ,"l'lrie' face oft said target 12 is located ina planefthat makes an angle of about 45 with the longitudinal axis of the'anode.` Surrounding the free end vof said anode and also located within the'envelope is a nickel-ironjscreen H13 ladapted tov prevent scattered electrons from striking on the inner walls of the envelope and/or to screenvout-undesirable X-rays and to house` the novel cathode structure 14. p f i l The screen consists-primarily of-fa cylindrical member l5 having a plurality of depressions-*or grooves vadapted to accommodate the teats .of

spring members 18.-` The upper end of said cylinder has a circumferential slot'in which is set an annular plate 16 of predetermined dimensions. This plate is of the same thickness and composition asrsaid cylinder and is secured to said cylinderby means of pins or thelike.-

`The annular Vplate 16 `hasa centralopening 17 through which someofthe Xrays generated at the anode .may travel unobstructedto theA en-` velope and therethrough totheouter atmosphere. The cylindrical member 15 has a 'circumy ferential' slot on the outer portion thereof and located near its bottom edge. Locatedain this slot' is a spring wire and also located in said slot below said spring'wireare the respective edges of the spring members '18, which-bear against the outery surface of the cylindricalrnernber and against therinner surface of the renvelope in order y to maintain the screen against longitudinalmovement." y"

secured to 'said plate `1e Ais' ametailic bushing i 19 'that is-in electrical contact therewith. AThis bushing 19 is also electrically connected to a leadin wirev 23 which is v-hermetically sealed .to'the envelope and electrically: connected to a zconta'ct terminal l(not shown). `Also secured to'said plate nected to a contact terminal (not shown).

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the :focusing cup. The cone 16 and located in an opening thereof is an insulating bushing 20. An electrical conducting lead Wire 24 extends through an opening of said bushing 20 and has one end thereof like the lead wire 23 hermetically sealed to the envelope and con- The other end of said lead Wire 24 is electrically connected Yto a cathode as hereinafter described.

` The novel cathode lstructure 14 comprises essentially a focusing cup in which is mounted a cathode associated with a cooling and defiectmay be assembled as shown with the mouth of -the lfocusing cup being at a relatively small acute Yangle to the target face of the anode. With this construction itis possible to obtain an annular ing pin and an electron shielding means. vThe focusing cupV comprises a plurality of vmetallic cylinders 30 and 31 Vunitedto each otherbya iiange 32, with the cylinder 30 having a diameter.

about one-half that of the cylinder 3l. The outer end of the cylinder 31 has cut out portions 33 of small depth and about ".1 of the depth'of the cylinder 31 and whose lengths are about'onefourth the peripheral dimension of said cup 31. These cut out portions`n33 are in'opp'osite diametrical relationship. Y

.Mounted in the small? diameter cylinder30 is aA thermionicA element or cathode '34- which'may be composed of tungsten, tantalu'mwor 'the like. This cathode '34' may be of flamentary form and of appropriate 'length andA cross section =to supply the necessary electron emission-When heated to a predetermined temperature byY means of a source of potential (notshown);

The filamentary cathode 34 may consist of aboutl seven' andone-half turns and is spirally wound so that it-simulat-es a cone madefup of a plurality of` spaced coi-ls. 'One end of theffilament, Vand as shown vrthe end thereof atthe base of the cone, is-securedfto the cup 30 vso as to be in electrical contact therewith. {The other vend of the filament at the fapex of the cone extends along thel altitude of the cone. V-Asubstantial length of said filament extends'along, is Wound around and is in contact with substantially -the entire length'of the solid cooling and electronrdefl'ecting pin 35.

` `This pin' 35 may be composedof molybdenum and has a diameter about five times `the Acorresponding dimension of the filament 34. Thepin extendsalong the altitude ofthe coneY and has one end located approximately vin the space described by Vthe topmost turn of thefilament 34.

The cathode lassembly consisting ofthe coiledfilament 34 and the pin'35v is somounted, with one endof the'filament Welded to thecylinder 30 and the pin" vveldedly secured to a support and'conductor'd; that the altitudeV of thecone defined by the pin is substantially in the center of and coincidentA With-"the longitudinal axis of u Y Y or coiled filament and pin are so-located insaid cup that the pin issubstantially fflush With'the topmost coilV of the cone and 'aboutffk mmfab'ove the top of the flange`32. `Securedto `the inner' surface of said cylinder 30 Aand withV its upper portion located about/1 mm; below the top of the.V flange 32is` an annular ring of L shaped cross Vsectional configuration.l Y f One side 37 thereof in the'form of a ring-is contiguous' with the inner surface of the cylinder 30 and the other side 38 thereof is substantially perpendicularto theflongitudinal Jaxis of the cylinder 30. The-'side 38 is' closely adjacent but notcontacting-the second turn of thefilament 34 tosubstantially'r completely shieldlthe' lastY two turnsof said filament-so that the 'electrons emahating from theselast twoturns-fare prevented `virtue of its being connected also vto the lead 24 and insulated from the plate 16.

:This cathode structure as heretofore described focal spot with 'no center spot because the innermostturn or turn and a half of the filament are cooled so that the electron emission therefrom is vmaterially less than that of the remaining portion of the filament, and because the outermost tvvo turns or soV ofthe filament are shielded by means of theshielding arm 38 to prevent the electrons emanating 'from Ithese turns of the filamentl from `reaching the anode. Thus relatively none'of Vthe electrons that strike'lthe targetV are derived from `the firstfturn or the last two turns of-the filamentwhen aworking potential is applied between the anode and cathode. vThe invention. is susceptible to modifications and the scope thereof .is to be limited only by the prior art. Y

iWhat is'claimed: Y

1. An X-ray tube comprising an envelope,an anode and a cathode structure therein, said anode having a target disposed at an acute angle to the longitudinal axis of said envelope, an electron shield having an opening therein through which X-ray's may emerge. said cathode structure-being supported by said screening means which' is located Within' saidy envelope, said cathode structure' including `a'focusing cup and a spiral filament, said filament being located in said cup and having the apexl thereof directed towards' said target, a shielding means electrically connected to said focusing` cup and located adjacent one turn of said filament for preventing the electrons emanating at said turn upon filament incandescence from Areaching said anode. Y

2. An X-ray tube comprising an envelope,an anode, a cathode structure and an X-ray screening means located in said envelope, said X-ray screening means housing said cathode structure and that end of the anode carrying the target, said cathode structure being supported by said screening means and including a focusing means, a spiral filament'and a cooling and deflecting pin, said spiral filament being in electrical series relationship with said focusing means and said pin, said pin extending along the altitude of said spiral filament, a shieldingmeans supported by said focusing means and located between the face of the target and one turn of said filament to prevent the electrons emanating at that turn upon filament incandescence from striking the anode.

3. A cathode structure comprising a focusing cup Vand a filament located therein, said focusing cup including a plurality of concentric means, one of said means being of largerdiameter than said other .means and. being connected to said other means, said filament having a portion thereof located in said other means, the outer limit of said means of Vlarger diameter having va plurality of cut-outs therein.V v I 44.v Alcathode structure r comprisingI a focusing cup having a mouth, a' spiral filament simulat- 'said turnv upon filament incandescence from traveling to the mouth of said cup, said one turn of said filament being located below said means, and a plurality of other turns of said filament located above said means.

5. A cathode structure comprising a focusing cup having a mouth, a spirallament mounted therein, and having one end thereof connectedr to said cup, shielding means secured to the inner surface of said cup and being electrically connected thereto, said shielding means being closely adjacent one turn of said fllament for preventing any substantial quantity of electrons emanating at said turn upon filament incandescence from traveling to the mouth of the cup, said shielding means being located appreciably below the mouth of the cup and a' cooling and deflecting pin extending along the altitude of said spiral filament, one end of said pin being located in the space described by the uppermost turn of said filament, said spiral'filament simulating a cone said turn of said filament being located below said shielding means and some otherof.' the turns of said filament being located above said shielding means.

f CLAYTON TRIDLE ULREY. 

